1. Field of the Invention
The present invention relates to a fuel supply system, and more particularly to a fuel supply system for an off-road vehicle such as a four-wheeled buggy having wide tires on front and rear wheels for running over rough terrain such as prairies and deserts.
2. Description of the Relevant Art
In recent years, there are manufactured and used off-road vehicles such as four-wheeled buggies having wide tires on front and rear wheels for travel over rough terrain such as prairies and deserts. One example of such off-road vehicle is disclosed in Japanese Utility Model Publication No. 54-19606 published July 19, 1979 which was filed by the assignee of the present application. The disclosed off-road vehicle comprises a vehicle frame, a driver's seat disposed centrally in the frame, an engine mounted on the frame between the driver's seat and a rear wheel axle, a fuel tank and a transmission case which are relativley heavy and disposed rearwardly of the engine on respective sides of the vehicle frame. A carburetor is located behind the engine. The heavy components such as the engine, the fuel tank, and the transmission case have their centers of gravity positioned near the rear wheel axle.
Since the fuel tank is located rearwardly of the engine on one side of the frame and the carburetor behind the engine, an air cleaner case is disposed rearwardly of the engine parallel to the fuel tank across the vehicle frame. Therefore, the air cleaner case is normally situated closely to an exhaust pipe extending rearwardly from the engine, and hence is susceptible to the heat of the exhaust pipe. The connecting pipe between the air cleaner and the carburetor is also disposed rearwardly of the engine. Accordingly, many pipes or tubes are closely packed in the space rearward of the engine. As a result, air circulation for cooling the engine and the radiator is poor. The volumes or capacities of the fuel tank and the air cleaner are limited by their parallel arrangement transversely across the vehicle frame.
Many general off-road vehicles have a vehicle frame composed of a plurlaity of mutually welded pipes. The engine, the fuel tank, and other parts are supported on such a vehicle frame of welded piping. Particularly, the fuel tank is often suspended from or disposed astride of a pipe through a skid plate or the like. The pipe by which the fuel tank is thus supported is therefore required to be higher is ridigity than the other pipes of the vehicle frame. It is necessary that the fuel tank supporting pipe be of an increased wall thickness or of a reduced length. Consequently, the vehicle frame is increased in weight or can be designed only with limited freedom or flexibility.
On four-wheeled off-road vehicles of the type described above, and two- and three-wheeled off-road motorcycles, the fuel inlet port of the fuel tank is generally closed by a removable cap which has a lock mechanism for locking the cap to the fuel tank. The cap has a key slot defined in its upper surface for insertion therein of a key for operating and releasing the lock mechanism, and a key cover for selectively closing the key slot.
The key cover is usually disposed such that it rotates about an axis normal to a plane containing the upper surface in which the key slot is defined. This key cover arrangement often results in the tendency that after the fuel tank has been refilled, the cap may be attached to the fuel tank again while the key slot is not covered by the key cover. As a consequence, water droplets, muddy water, dust, and/or other foreign matter may be deposited in or enter the key slot, and the key slot may be clogged by the unwanted deposit. One solution is to use a spring for urging the key cover to the key slot closing position. The spring must produce a relatively large spring force to slide the key cover over the key slot. When opening the key cover, therefore, a large force is required to rotate the key cover against the resiliency of the spring. Once foreign matter such as small stones is caught between the key cover and the key slot, the key cover gets stuck and will not rotate in either direction.
The off-road vehicles run over rough terrain such as prairies and deserts at high temperature during summer. As described above, the fuel tank is disposed rearwardly of and closely to the engine, and is directly exposed to sunlight as it is not covered by a cover. Therefore, the fuel tank is subject to hot air over the rough terrain, the heat of the engine, and strong sunshine. If an off-road vehicle employs a pressure-feed fuel system having a fuel pump, as with two-wheeled, on-road motorcycles, then vapor lock is apt to occur in the fuel line from the fuel tank to the carburetor. If a gravity-feed fuel system is incorporated in an off-road vehicle, on the other hand, such a vapor lock condition in the fuel line is avoided because the fuel tank is positioned more or less higher than the carburetor. The gravity-feed fuel system, however, does not have a large fuel supply capability. With the fuel tank in an elevated position, the center of gravity of the vehicle as a whole is also elevated, which is not preferable for off-road vehicles and is disadvantageous from the standpoint of layout of the fuel tank.
On four-wheeled off-road vehicles, a fuel shutoff valve is disposed in the fuel line in the vicinity of the fuel tank, as with two-wheeld on-road motorcycles. Inasmuch as the fuel tank is disposed rearwardly of the engine behind the driver's seat, as described above, it is difficult for the driver seated on the driver's seat to operate the fuel shutoff valve.
It is an object of the present invention to provide an off-road vehicles which will overcome the aforesaid problems of the conventional off-road vehicles.